Certain ships can only be built with the express permission of the Crown. In order to command this ship, take this uncertified deed, along with the correct Writ, to your national Capital to have your deed certified
Unlike the 'Indomitable' First Rate and 'Victory' First Rate, the Writ for the 'Sovereign' First Rate can ONLY be purchased in Treasure Aisle (TA) for 1300 Burning Sea Points (BSP).